The art of glass shewing how to make all sorts of glass, crystal and enamel : likewise the making of pearls, precious stones, china and looking-glasses : to which is added, the method of painting on glass and enameling : also how to extract the colours from minerals, metals, herbs and flowers ... : illustrated with proper sculptures / written originally in French, by Mr. H. Blancourt, and now first translated into English ; with an appendix, containing exact instructions for making glass-eyes of all colours.

CHAP. LXXIX. To make in Natural Crystal the Colour of Rubies, Topaz, Opal, Gyrasol and others.

IT seems something strange that Crystals mixed with Matters that tinge it, should in the same Vessel receive so many different Colours. But if you consider that the Spirits of these Matters, have Vir∣tues different from those of their Bodies, you will not so much wonder at such Diversities. The Pieces which lie highest, are the most penetrated by these tinging Spirits which always ascend, and so give them more vivacity and colour; and so to the others in proportion to your Orders.

For this Operation, take two Ounces of Orpiment of a yellow Colour approaching Gold or Saffron, and as much White Arsenick; one Ounce of crude An∣timony, and the same weight of Sal-Armoniac; the whole reduced to Powder and mixed together. With this Powder stratifie pieces of Natural Crystal in a great Crucible, putting the least pieces to the bottom, and the greatest at the top which ought to be fine and without Spots. The Crucible being fill'd with the Powder and Crystal, cover it with another bored at the bottom, lute them well and let the lute dry. This last Crucible must (as we have said) be bored at bottom, that the smoak of the Materials as∣cending through the Hole, may better tinge the Crystals in passing, which it would not do so well if it passed out of the sides. When the Lute is dry, put it in the Furnace, and cover it with Coals up to the middle of the Crucible on the top, then put some live Coals to them, that they may kindle ••y themselves

little by little, they ought to be great Coals, and made of Oak. You must take care of the Smoak, it being very dangerous, as we said before; and order it so that they kindle well, that the Business may suc∣ceed, and that the Fire may go out of it self, taking care that no Air can get in at the Mouths of the Cru∣cibles, for that would make the Crystals break, and then they are good for nothing.

The Crucibles being cold unlute them, and take the Crystals out, the greatest parts of which will be tinged with the colours we have mentioned: Polish the best colour'd at the Wheel, which will also brighten their Colours, and make them look like Oriental Stones, and they'll be fair and hard as they are.

All the Success of this Secret consists in the Orpi∣ment, which must be of the colour of Gold; and if you don't succeed the first time, you must try a se∣cond; and observing well what we have said, you may be assured to succeed.

The End of the Third Book.